A microwave plasma processing apparatus in the related art uses high density plasma excited by a microwave electric field. For example, the microwave plasma processing apparatus includes a planar antenna having a plurality of slots which are arranged to generate uniform microwaves. In the microwave plasma processing apparatus, microwaves are radiated from the slot antenna to the inside of a processing container and ionize a gas within a vacuum container so as to excite plasma. See, for example, Japanese Patent Laid-Open Publication Nos. H9-63793, H3-191074, and 2007-213994.